Coated abrasives for electrolytic grinding



April 9, 1968 B. w. DUKE ET A 3,377,264

COATED ABRASIVES FOR ELECTROLYTIC GRINDING Filed Nov. 5, 1964 ML r 3/ 35 BRUCE [NV 93%: CH RL s \KLBARSHALL ATTORNEY Uiffi SE ABSTRACT OF THE DISCLOSURE A coated abrasive product having a non-conductive backing carrying a plurality of adhesively-bonded, nonconductive abrasive grains on one face and an overlying conductive layer on top of said abrasive grains. When used in electrolytic grinding, the abrasive grains protrude through the electrically conductive layer.

The present invention relates generally to coated abrasives and more specifically to coated abrasives in the form of discs, belts or the like especially adapted for use in electrolytic grinding operations.

Electrolytic grinding, or the electrolytic removal of material from an electrically conductive workpiece augmented by contact between the workpiece and an abrasive grinding tool has long been a recognized area of use for metal-bonded abrasive wheels. Only very recently have efforts been made to supplant the bonded wheel by a coated abrasive disc or belt in order to gain the advantages of the coated products ability to conform to irregular surfaces and the increased abrasive area of a belt as contrasted to a wheel. Metal-bonded wheels have been quite limited as to both shape and size, keeping the electrolytic grinding process in consequence limited to a relatively small area of the metal grinding field.

Accordingly, it is an object of the present invention to provide a coated abrasive construction suitable for use in electrolytic grinding.

Another object of the invention is the provision of coated abrasive articles for electrolytic grinding having improved conductivity over those known to the art.

Additional objects, if not specifically set forth herein will be readily apparent to one skilled in the art from the following detailed description of the invention.

In the drawings FIGURE 1 shows a cross-section of a coated abrasive belt formed in accordance with the present invention.

FIGURE 2 illustrates a cross-section of a coated abrasive disc made in accordance with this invention.

Generally, the present invention contemplates the use in an electrolytic grinding abrasive of a water-resistant, non-conductive backing, preferably in the form of woven textile fibres, to which backing, in any manner well known in the coated abrasive art is firmly anchored a plurality of non-conductive abrasive grains. The adhesive or adhesives used in anchoring the grains to the backing are non-conducting electrically and are designed to give maximum anchorage between the abrasive grains and the backing during wet grinding operations. Laminated or bonded to the abrasive coated face of the non-conductive backing is a layer of conductive material through which the tips of the abrasive grains protrude.

The prior art has suggested the use of relatively inflexible woven or perforated metal backings, i.e., completely conductive backings which have very poor life when subjected to the flexing inherent in their use, for example, as an abrasive belt. The use of conductive adhesives has also been suggested. In this type of adhesive tes Patent the holding power of the adhesive is weakened in order to obtain conductivity and the resultant abrasive product is a poor compromise which will not hold up well in use. An improved, but still complicated, type of electrolytic grinding material in the form of a coated abrasive is described and claimed in the copending application of Dyer et al., Ser. No. 392,741, filed Aug. 28, 1964, now Patent No. 3,334,041.

More specifically it has now been found that if a conventional coated abrasive belt, disc or the like is made on a woven textile backing using a good water-resistant maker adhesive, e.g., phenolic resin and a good size adhesive, e.g., phenolic resin, as has been heretofore known in the art the resultant belt or disc has the requisite life and grain adhesion required for good performance. Such belt or disc may be converted for electrolytic grinding by forming a conductive layer on the front surface only thereof (with the non-conductive abrasive grains protruding through the front conductive layer) and providing means in the grinding machine on which such belt or disc is to be used for conducting electric current to such front conductive layer. The resultant belt or disc will compare favorably for flex life and operating life with a conventional abrasive belt or disc and will give excellent results in electrolytic grinding operations.

Generally, the front conductive layer is either a laminated foil or a coating of metal applied directly to the abrasive surface as by metal spray, vacuum metallizing, electroplating or the like. In any instance, care must be taken before actual electrolytic grinding commences that the abrasive grain tips (which are non-conductive) do, in fact, protrude from the film or metal coating layer. This may be accomplished by mechanical abrasion or by deplating, i.e., mounting the metallized coated abrasive article in the electrolytic grinding machine and reversing the current flow to plate the metal from the tips of the grain onto a dummy workpiece. Since the abrasive tips are the highest point in the plane of the abrasive article,

this step of clearing the tips is relatively uncomplicated.

Referring now to the drawings, FIGURE 1 illustrates a cross-section of an abrasive belt 10 composed of a non-conductive woven backing member 11 having a front surface 12 and a back surface 13. A layer of abrasive grains 14 is bonded to the front surface 12 of belt 10 by a water-resistant adhesive 15, such adhesive 15 and abrasive 14 being applied in the form of a strip 16 along the length direction of belt 10. Over the entire front surface 12 including abrasive grains 14 is applied an electrically conductive foil 17. This foil 17 is adhered to the abrasive-coated strip 16 and to the non-abrasive edges 18 of front surface 12 by a suitable adhesive 19 as is more fully described below. It will be noted that the abrasive grain. 14 is shown protruding through the foil 17. This may be accomplished in the laminating procedure but if not can be done by deplating or mechanical abrading as described above. The foil may be any conductive metal foil such as aluminum, copper, tin, lead or the like and has been used in thicknesses ranging from .00065" to .005 in thickness. Heavier foils can be used if desired although the range given above appears to be adequate. The foil is applied to the front or abrasive side 12 only of the woven non-conductive backing strip 11 after lightly sizing the abrasive coated strip 16 and the non-abrasive coated edges 18 with a suitable Water-resistant adhesive 19. The specific adhesive is not critical and one which has been found effective is a blend of epoxy ester and polyamide resin in methyl ethyl ketone solvent. These materials are commercially available as Epon 1001-X- and Versamid 140. A 1:1 blend of these components with 15% methyl ethyl ketone solvent added produces a good laminating adhesive. After placing the foil on the adhesivecoated surface the laminate is run through a set of pressure rolls, one steel and the other rubber (Shore A-2 hardness45) with the abrasive surface towards the rubber roll. Air operated pistons supply a pressure of 15 pounds per inch of roll width to force the foil into intimate contact with the adhesive-coated surface. Following laminating the material is wound on a core of not less than 16" diameter with the abrasive-foil surface convex to insure no separation of foil will occur. The material is then cured for 16 hours at 135 F. followed by /2 hour at 175 F., /2 hour at 200' F., /2 hour at 225 F. and a final /2 hour at 250 F.

Extending through the belt in the area of the abrasive coated strip 16 are a plurality of perforations 20 to provide adequate electrolyte flow through the belt when in use. These may vary in size and number as desired, but preferably are of 4;" diameter and are arranged in a staggered pattern offset from the web direction in order to prevent marking the workpiece with a pattern when the belt is used in electrolytic grinding.

FIGURE 2 shows another modification wherein a disc is formed from a non-conductive woven textile backing 31 with a layer of non-conductive abrasive grain 32 bonded to the front surface 31 thereof by a nonconductive, water-resistant adhesive 33. A conductive layer on the front surface only of the disc 30 is provided in this modification by the application over the adhesive 33 and grain 32 of a metal coating to form a layer of metal 34 adhered thereto.

In applying the metal coating various techniques i known to the art of metal application may be used including flame spraying, vacuum metallizing, plasma are or the like. Generally it is desirable to sandblast or otherwise roughen and clean the surface of the disc before applying the metal to insure proper adhesion. It has been found that a conductive layer of metal has sufiicient adhesion to prevent metal shedding when the coated discs are run wet on a conventional grinding machine under 80 psi. workpiece pressure. Copper has been found to be the preferred metal since the adhesion is much higher than that of sprayed zinc or aluminum. The thickness of the sprayed metal layer should range from about .005" to 0.02". Good results have been achieved using a coating of 0.008 on the front surface of electrolytic grinding discs. The spray-applied metal must be removed from the tips of the non-conductive abrasive particles before use in an electrolytic grinding process and, as described above, this may be done by deplating or mechanical abrasion.

One or more holes such as illustrated by reference numeral 35 are provided in the disc to permit passage therethrough of a spindle or mounting bolt (not shown) which will conduct the electrical current to the front metal coated surface 34 of disc 30. A conductive washer of copper or the like around such bolt and held to the face of disc 30 by a nut on the bolt is usually used to transmit the current. In use the disc is mounted on a steel flange which is substituted for the usual grinding wheel in a conventional electrolytic grinding unit. The bolt or bolts holding such flange in place on the wheel spindle are preferably used to transmit the current to the face of the disc. In addition, while the disc 30 may be perforated for coolant flow, generally it is not and the coolant is applied to the abrasive side only.

The following specific examples are illustrative of the performance in electrolytic grinding operations of belts and discs made in accordance with the present invention:

Example 1 Belts according to the construction illustrated in FIG- URE l were prepared by taking; conventional, resinbonded, water-resistant coated abrasive materials (Grit 60, Speed-Wet Metalite Cloth) which were made on X weight cotton, desized drills cloth using a phenolic resin maker and size adhesive. The material coated was 4' in width and the maker adhesive, abrasive grain and size adhesive was applied in a 1 /2" wide strip running lengthwise of the 4" wide backing. Laminated to the entire coated side of the 4" material Was a layer of .001" 1235ODry aluminum foil, applied as described in connection with FIGURE 1. The center coated area only was then perforated with a pattern of A5" holes on centers, in staggered array, off-set 4 from the web direction to prevent ridging or patterning of the workpiece. Belts measuring 4" x 107" were cut from this material and joined by cutting the ends at angle and adhering such ends to each other to form a single skive adhesive joint in conventional fashion.

These belts were used in electrolytic grinding of V2" square stock M-2 Star-MO High Speed Steel workpiece, hardened to Rockwell C65, using an electrolytic belt grinding machine. This equipment generally is of the type disclosed in U.S. Letters Patent No. 2,997,- 437 to Richard A. Whitaker and more specifically as disclosed in Canadian letters Patent No. 689,815. The belt tension in each case was 45 the belt speed was 1150 surface feet per minute and the voltage was 7.0 volts DC. The electrolyte was #SO90, 2#/ gal. solution delivered at the rate of 5 gallons per minute filtered. Electrical cont-act to the conductive edges of the belt Was provided by brushes in contact with the foil. The following results were achieved:

Flame-sprayed metal coated discs as illustrated in FIGURE 2 were made by first applying a layer of pressure sensitive adhesive to the back surface of conventional Grit Speed-Wet Metalite Cloth abrasive material followed by the application of a release-coated paper liner to such adhesive surface. Six inch diameter (1%." center hole) discs were stamped from this material and, using a separate die set-up, four mounting holes of diameter were punched through the discs on 2%" centers about a circle of 1 /8" radius from the disc center holes. The abrasive surfaces of the discs were sandblasted using a Vacu-Blast Jr. sandblasting unit and aluminum oxide grain. Sandblasting was continued only long enough to de-lustre the material. Then the front surface only of the abrasive material was flame-sprayed with copper using a Metco Type 4-E metallizing gun. The gun was hand held and was directed at the surfaces of the discs in a manner similar to that used for manual paint spraying. These discs were run on a EGD-7 machine. A steel flange was mounted on the wheel spindle of this machine and after the discs were aligned with the mounting holes on the wheel flange, they were anchored in place by the pressure sensitive adhesive back coating (the liner being first removed). Electrical contact with the surface layer of sprayed metal was obtained by the use of soft copper washers under the heads of the mounting screws, providing a current path through the Wheel spindle to the wheel flange and then through the mounting screws and copper washers to the sprayed metal surface. Test results were as follows:

Room temperature: 74 F.

Workpiece: /2 square (.25 in?) Circle C Tool Steel Power supply: 7.5 v.; Spark suppress40 Deplating: 7.5 v.', Spark suppress40 Machine speed: 5500 s.f.p.m.

Electrolyte: NaCl, 2#/gal. applied to front of disc Air cylinder feed: v

Time (min) Avg. Current; Linear Mils Metal Removed (amps) Removed (111.

. 5 200 50 1 5 225 (it) l2 5 200 50 l 5 200 50 l 5 225 50 1 5 200 50 l 5 2-25 50 l 5 225 50 I 5 225 50 l 5 225 50 1 1 Adjusted [010110 minute on l in test bar. 2 Same as A except here the wheel was oscillated.

The abrasive grain, abrasive grain binders and backings used in the present invention may be selected from any of the many known types used in the coated abrasive art. As indicated above, these components of 'the abrasive articles of the present invention or at least the front surfaces thereof must, however, be electrically nonconductive. The backing is preferably a woven structure but nonconductive films such as Mylar or the like, nonwoven backings, etc., may be used. While a flexible or semi-flexible backing is generally contemplated, it may be desirable in some instances to use a relatively rigid backing member, as for example a phenolic tube or the like. Likewise, while directed primarily to backing materials which are nonconductive throughout, circumstances might indicate the use of a conductive material covered in whole or in part with a nonconductive layer, as for example a steel shaft with a built-up section of nonconductive resin thereon. All such variations are contemplated within the scope of the present invention.

While the various constructions specifically described herein are preferred, obviously different electrically conductive coatings may be used as desired as can various widths, dimensions, perforations and other non-critical variations. The usual and preferred shape of the finished abrasive article is that of a flat disc or endless belt, but other shapes such as tubes, cylinders, sheets, blocks and the like can be used if desired.

Obviously, many variations and modifications can be made Without departing from the spirit and scope of the invention described herein, so that only such limitations should be imposed as are contained in the appended claims.

We claim:

1. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive backing material having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material; and

(C) An electrically conductive layer of material overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place.

2. A coated abrasive material as in claim 1 wherein said material is in the form of an endless belt.

3. A coated abrasive material as in claim 1 wherein said material is in the form of a flat disc.

4. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible backing ma terial having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material; and

(C) An electrically conductive layer of material overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place.

5. A coated abrasive material as in claim 4 wherein said material is in the form of an endless belt.

6. A coated abrasive material as in claim 4 wherein said material is in the form of a flat disc.

7. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible backing material having a front surface and a back surface;

' (B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material; and

(C) An electrically conductive layer of metal overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place.

8. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible backing material having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material; and

(C) An electrically conductive layer of foil overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive foil when electrolytic grinding is taking place.

9. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible woven backing having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material;

(C) An electrically conductive layer of material overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place; and

(D) A plurality of perforations extending through said electrically nonconductive backing and said electrically conductive layer bonded thereto.

10. A coated abrasive material as in claim 9 Wherein said material is in the form of an endless belt.

11. A coated abrasive material as in claim 9 wherein said material is in the form of a circular disc.

12. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible woven backing having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material;

(C) An electrically conductive layer of foil overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive foil when electrolytic grinding is taking place; and

(D) A plurality of perforations extending through said electrically nonconductive backing and said electrically conductive layer bonded thereto.

13. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible woven backing having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material;

(C) An electrically conductive layer of sprayed metal overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place; and

(D) A plurality of perforations extending through said electrically nonconductive backing and said electrically conductive layer bonded thereto.

14. A coated abrasive material especially adapted for electrolytic grinding which comprises:

(A) An electrically nonconductive flexible woven backing having a front surface and a back surface; (B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material;

(C) An electrically conductive layer of vacuum deposited metal overlying said front surface only and bonded thereto, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place; and

(D) A plurality of perforations extending through said electrically nonconductive backing and said electrically conductive layer bonded thereto.

15. An electrolytic grinding belt which comprises:

(A) An endless band of electrically nonconductive flexible backing material having a front surface and a back surface;

(B) A plurality of electrically nonconductive abrasive grains adhesively bonded to the front surface of said backing material in the form of a strip centered along the median line of said endless band, leaving uncoated margins on said endless band; and

(C) An electrically conductive layer of material overlying said front surface only and bonded thereto, said layer covering said strip of abrasive grain and the uncoated margins of said endless band, said abrasive grains protruding through and above said electrically conductive layer when electrolytic grinding is taking place.

References Cited UNITED STATES PATENTS 2,820,746 1/1958 Keeleric 204-16 2,858,256 10/1958 Fahnoe et a1. 20416 XR 3,162,588 12/1964 Bell 204224 XR 3,317,416 5/1967 Warren 204-290 3,334,041 8/1967 Dyer et Ell. 204-284 JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

D. R. JORDAN, Assistant Examiner. 

